LONG-TERM VERB CODE SIMULATIONS OF ULTRA-RELATIVISTIC ELECTIONS AND COMPARISON

WITH VAN ALLEN PROBES MEASUREMENTS

Drozdov A. Y.1,2, Shprits Y. Y.1,3, Orlova K.G.1,2, Kellerman A. C.1, Subbotin D. A.1, Baker D. N.4, Spence H.E.5 and Reeves G.D.6

1. University of California, Los Angeles, CA, USA2. Lomonosov Moscow State University Skobeltsyn, Institute of Nuclear Physics, Moscow, Russia3. Massachusetts Institute of Technology, Cambridge MA, USA4. Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA5. Institute for the Study of Earth Oceans and Space, University of New Hampshire, Durham, NH, USA6. Space Science and Applications Group, Los Alamos National Laboratory, Los Alamos, NM, USA

Comparison of 1D simulationsSep, 07 – 19, 2012

Comparison of the diffusion coefficients

Reproduce 1D simulation performed by Thorne et al. [2013]

“We demonstrate that the slow temporal decay of the electron ring for energies above 3 MeV is caused by pitch angle scattering due to the global distribution of plasmaspheric hiss”

Results of simulation by the VERB code

Results of simulation from Thorne et al. [2013]

Long period simulationOct 2012 – Oct 2013

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tions

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onKp

DST

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onFlux. Energy 0.9 MeV. L* vs time plot.

PSD. = m 700 MeV/G. L* vs time plot.

Reproduce the dynamics of relativistic electrons, but not for the ultra-relativistic energies

Flux. Energy 3.6 MeV. L* vs time plot.

𝜏𝑉𝐸𝑅𝐵=6 .1𝑑𝑎𝑦𝑠 ,𝜏𝐷𝑎𝑡𝑎=3 .8𝑑𝑎𝑦𝑠

Decay rates comparison at L*=4Oct, 01 – Nov, 30, 2012

𝜏𝑉𝐸𝑅𝐵=2.1𝑑𝑎𝑦𝑠 ,𝜏𝐷𝑎𝑡𝑎=4 .0𝑑𝑎𝑦𝑠

Energetic electrons. 300 keV Relativistic electrons. 900 keV Ultra-Relativistic electrons. 3.6 MeV

𝜏𝑉𝐸𝑅𝐵=95 .5𝑑𝑎𝑦𝑠 ,𝜏𝐷𝑎𝑡𝑎=9 .4𝑑𝑎𝑦𝑠

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=4

Observed and modeled decay rates are significantly different for ultra-relativistic electrons

Drozdov, A., Y. Y. Shprits, K. G. Orlova, A. C. Kellerman, D. A. Subbotin, D. N. Baker, H. E. Spence, G. D. Reeves (2015), Energetic, relativistic, and ultrarelativistic electrons: Comparison of long-term VERB code simulations with Van Allen Probes measurements, J. Geophys. Res. Space Physics, 120, doi:10.1002/2014JA020637.

1D, 2D and 3D simulationsOct, 21 – Nov, 12, 2012

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Neither of 1D, 2D, 3D simulations can reproduce the dynamics of ultra-relativistic electrons

Observations

Only pitch-angle scattering (no sources)No radial diffusionFull simulation

L* = 4

3D S

imul

ation

Hiss, EMIC waves?

Discussion of possible loss mechanisms

Bw2 observed and used in Dαα calculations

Latitude and L* dependence.Orlova at al., 2014

Accurate determination of such parameters as wave amplitude, power spectral density, wave normal angle, plasma pause location, plasma density are important for computing the diffusion coefficients.

Dat

aM

odel

Average spectrum for the Hiss wavesObserved and used in the Dαα

calculations

Calculated Dαα with various lower

frequency cutoffDecay rates.

Courtesy of Maria Spasojevic

Decay rates comparison at L*=4Oct, 01 – Nov, 30, 2012

Lower cutoff ~100 Hz

𝜏𝑉𝐸𝑅𝐵=95 .5𝑑𝑎𝑦𝑠 ,𝜏𝐷𝑎𝑡𝑎=9 .4𝑑𝑎𝑦𝑠

Obs

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tions

Sim

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onL*

=4Decay rates for different hiss diffusion coefficients.

Ultra-Relativistic electrons. 3.6 MeV

Lower cutoff ~40 Hz

𝜏𝑉𝐸𝑅𝐵=40 .3𝑑𝑎𝑦𝑠 ,𝜏𝐷𝑎𝑡𝑎=9 .4𝑑𝑎𝑦𝑠

EMIC waves are important!

The loss time scale for EMIC and hiss waves

Thorne and Kennel [1971]; Summers and Thorne [2003]; Li et al. [2007] Ukhorskiy et al., [2010] suggested that EMIC waves may provide efficient scattering mechanism for relativistic electrons.

Shprits et al., 2014

Bounce-averaged pitch-angle diffusion coefficient for the EMIC waves

Ukhorskiy et al. 2010

Conclusions

• Comparison of VERB code simulations with Van Allen Probes observations shows relatively good agreement for relativistic and energetic electrons.

• At higher energies, modeled fluxes of ultra-relativistic electrons show much slower decay rates than seen in observations.

• Comparison of simulations with observations show that the EMIC waves is likely a major additional mechanism of the ultra-relativistic electrons scattering that needs to be included into simulations.

BACKUP

Simulations with EMIC wavesMar, 06 – 16, 2013

Ma et al. [2015]

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3.60

MeV

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60 M

eV

Reproduce the results

Preliminary

When Kp ≥ 2 EMIC, Bw2 = 0.1 nT2 (Bw = 0.32 nT)

Bw = 1 nT [e.g. Ukhorski et al, 2010; Min et al. 2012]

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60 M

eV

Preliminary

EMIC waves are tricky

EMIC Daa

Long period simulationOct 2012 – Oct 2013

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onKp

DST

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tions

Sim

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onFlux. Energy 0.9 MeV. L* vs time plot.

PSD. = m 700 MeV/G. L* vs time plot.

Reproduce the dynamics of relativistic electrons

Long period simulationOct 2012 – Oct 2013

Flux. Energy 3.6 MeV. L* vs time plot.

PSD. = m 3500 MeV/G. L* vs time plot.

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DST

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There is a discrepancy at ultra-relativistic energies